1. Field of the Invention
The invention relates to a multilayer circuit board or a multilayer wiring board and a semiconductor device and, more particularly, to a multilayer circuit board having improved heat-dissipating properties and a semiconductor device using it.
2. Description of the Related Art
Among multilayer circuit boards used for semiconductor devices, there are products in which a metal substrate is used as a core substrate, and wiring layers are stacked on either side of the core substrate, each of the stacked wiring layers being isolated from an adjacent wiring layer by an insulating layer interposed therebetween. The stacked wiring layers can be formed on either side of the core substrate by a build-up process. According to a build-up process, a multilayer circuit board, in which one wiring layer is electrically connected to another wiring layer by vias through the insulating layer, can be obtained by forming an insulating layer electrically insulating wiring layers from each other and having via holes for the interconnection of the wiring layers, forming a conductor layer on the surface of the insulating layer and the inside of the via holes by plating or the like, and then etching the conductor layer in a given pattern.
A semiconductor device is produced by mounting, on the multilayer circuit board thus formed, a semiconductor chip or chips and required circuit parts. In recent years, semiconductor elements have had increasingly improved performances, thereby increasing the amount of heat generated therefrom. Conventional methods for dealing with an increased amount of heat generated from such a semiconductor element include a method of dissipating the generated heat by attaching a heat spreader (or heat sink) to the semiconductor element and using a fan. Also, a metal sheet with good heat-dissipating properties is used as a core substrate in order to improve the heat-dissipating properties of a multilayer circuit board on which a semiconductor element is mounted.
However, even with a multilayer circuit board using a metal sheet for a core substrate, the heat-dissipating properties are not always enough considering the increasing amount of heat generated from a semiconductor element, and a multilayer circuit board having better heat-dissipating properties is required to remove the heat generated from a semiconductor element.
It is known to use a member made of a metal to cover a semiconductor element mounted on a multilayer circuit board, to thereby dissipate heat generated by the semiconductor element from the top face of the metallic member to environment. Again, with a multilayer circuit board using such a cover member, heat-dissipating properties are not always enough to increase amount of heat removed from a semiconductor element, and a multilayer circuit board having improved heat-dissipating properties is again required.